Methods and apparatus for detection system having fusion of radar and audio data

ABSTRACT

Methods and apparatus for locating a weapon by fusing audio and radar data. An exemplary embodiment comprises detecting a weapon firing event with an audio sensor system, detecting a projectile fired from the weapon with a radar system, calculating a state vector associated with the projectile detection, identifying a location of the weapon by backtracking the state vector to the detected time of the weapon firing event time, and communicating the location of the weapon.

BACKGROUND

Radar systems transmit electromagnetic radiation and analyze reflectedechoes of returned radiation to determine information about thepresence, position, and motion of objects within a scanned area.Conventional weapon locating systems include a radar system that candetect and track projectiles, such as artillery projectiles, todetermine the location of the fired weapon. This determination can bebased on an extrapolation of estimated state vectors, derived by radartracking of a ballistic target, to a point of intersection. Identifiedcoordinates associated with the intersection point approximate thelocation of the weapon that launched the projectile.

When the elevation angle of the bore of the fired weapon is smallrelative to the local earth tangent plane, conventional weapon locatingsystems are generally unable to accurately determine the location of theweapon. Such low angle trajectories produce exaggerated errors in thestate vector estimates. As the angle of elevation approaches zero, theintersection point on the terrain becomes indeterminate. At low angletrajectories, weapon location determination is also limited becauseprojectile detection and tracking by radar systems can be limited byimpaired lines of sight, radar multipath echoes, and clutter. Inaddition, the short track life of near-in fire with low angletrajectories creates difficulties in discriminating false targets. Whenthe location of the firing weapon cannot be accurately determined, theability to return precision counter fire or launch rockets at the firingweapon is impaired.

SUMMARY

Exemplary embodiments of the present invention provide method andapparatus to detect the firing location of weapons that fire projectileswith low angle trajectories. In exemplary embodiments, audio sensorinformation is fused with radar data to enhance the ability of thesystem to locate the location of a projectile firing system, such as arocket. While exemplary embodiments of the invention are shown anddescribed in conjunction with certain components, configurations,weapons, and the like, it is understood that alternative embodimentswithin the scope of the present invention will be apparent to one ofordinary skill in the art.

In one aspect of the invention, a method of locating a weapon comprises:detecting a weapon firing event with an audio sensor system, thedetected weapon firing event indicative of a detected firing of theweapon and indicative of a detected time of the weapon firing event,detecting a projectile fired from the weapon with a radar system,calculating a state vector associated with the projectile detection,identifying a location of the weapon by backtracking the state vector tothe detected time of the weapon firing event time, and communicating thelocation of the weapon.

The method can further include one or more of the following features:generating a common time base for the weapon firing event and for theprojectile detection, the audio sensor system comprises an audio sensor,the audio sensor system is directional and provides at least one of anazimuth angle of the detected weapon firing event or an elevation angleof the detected weapon firing event, the step of detecting the weaponfiring event with the audio sensor system comprises detecting the weaponfiring event by direct path detection of audio generated by the weaponfiring event, correlating the weapon firing event detected by the audiosensor system with the detection of the projectile by the radar systemto determine if the weapon firing event detected by the audio sensorsystem corresponds to the same projectile as that detected by the radarsystem, wherein the correlating comprises: selecting a time differencethreshold, and relating the time difference threshold to a differencebetween the detected time of the weapon firing event detected by theaudio sensor system and a time of the detection of the projectile by theradar system, the correlating comprises: selecting a time differencethreshold, and relating the time difference threshold to a differencebetween a time predicted by the state vector when backtracked to aterrain and the detected time of the weapon firing event detected by theaudio sensor system, the correlating comprises: selecting a positiondifference threshold, and relating the position difference threshold toa difference between a location predicted by the state vector whenbacktracked to a terrain and a location predicted by the state vectorwhen backtracked to the detected time of the weapon firing eventdetected by the audio sensor system, the correlating comprises:selecting an angle difference threshold, and/or relating the angledifference threshold to a difference between an angle to the projectileidentified by the radar system and an angle to the weapon identified bythe audio sensor system.

In another aspect of the invention, a weapon locating system comprises:an audio sensor system configured to detect a weapon firing event, thedetected weapon firing event indicative of a detected firing of theweapon and indicative of a detected time of the weapon firing event, aradar system configured to detect a projectile fired from the weapon, aprocessor configured to calculate a state vector associated with theprojectile detection and to backtrack the state vector to the detectedtime of the weapon firing event to identify the location of the weapon,and a communication system configured to communicate the location of theweapon.

The system can further include one or more of the following features:the processor is further configured to correlate the weapon firing eventdetected by the audio sensor system with the detection of the projectileby the radar system to determine if the weapon firing event detected bythe audio sensor system corresponds to the same projectile as thatdetected by the radar system, the processor is further configured toselect a time difference threshold, and relate the time differencethreshold to a difference between the detected time of the weapon firingevent detected by the audio sensor system and a time of the detection ofthe projectile by the radar system, the processor is further configuredto select a time difference threshold, and relate the time differencethreshold to a difference between a time predicted by the state vectorwhen backtracked to a terrain and the detected time of the weapon firingevent detected by the audio sensor system, the processor is furtherconfigured to select a position difference threshold, and relate theposition difference threshold to a difference between a locationpredicted by the state vector when backtracked to a terrain and alocation predicted by the state vector when backtracked to the detectedtime of the weapon firing event detected by the audio sensor system,and/or the processor is further configured to select an angle differencethreshold, and relate the angle difference threshold to a differencebetween an angle to the projectile identified by the radar system and anangle to the weapon identified by the audio sensor system.

In a further aspect of the invention, an article comprises: at least onecomputer-readable medium containing non-transitory stored instructionsthat enable a machine to perform: detecting a weapon firing event withan audio sensor system, the detected weapon firing event indicative of adetected firing of the weapon and indicative of a detected time of theweapon firing event, detecting a projectile fired from the weapon with aradar system, calculating a state vector associated with the projectiledetection, identifying a location of the weapon by backtracking thestate vector to the detected time of the weapon firing event time, andcommunicating the location of the weapon. The article can furtherinclude instructions for correlating the weapon firing event detected bythe audio sensor system with the detection of the projectile by theradar system to determine if the weapon firing event detected by theaudio sensor system corresponds to the same projectile as that detectedby the radar system.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawings illustrate embodiments of the devices andmethods disclosed herein and together with the description, serve toexplain the principles of the present disclosure.

FIG. 1 is a schematic diagram illustrating a weapon locating systemaccording to an embodiment of the present invention;

FIG. 2 is schematic diagram of a weapon locating system according to anembodiment of the present invention;

FIG. 3 is a diagram illustrating the trajectory of a projectile firedfrom a weapon;

FIG. 4 is a flowchart illustrating a method of locating a weapon usingan audio augmented weapon locating system having a radar system incombination with an audio sensor system according to an embodiment ofthe present invention;

FIG. 5 is a graph of down range error for an audio augmented and nonaugmented conventional weapon locating systems at various quadrantelevations; and

FIG. 6 is a schematic representation of an exemplary a weapon locatingsystem combing optical and/or audio sensor data with a radar system;

FIG. 7 is a schematic representation of an exemplary computer that canperform at least a portion of the processing described herein.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary weapon locating system 100 including a radarsystem 102 and an audio sensor system 104 that communicate signals to asignal processing system 106. The signal processing system 106 cantransmit information derived from the received signals to a responsesystem 108.

As described in more detail below, a conventional weapon locating systemhaving only a radar system can experience a reduced accuracy whendetecting and tracking weapons fired at low quadrant elevations (QE).Quadrant elevation (QE) is a commonly used artillery term to describethe angle between the gun or launchers elevation angle and localhorizontal. However when a conventional weapon locating system iscombined with an audio sensor system, data generated by the combinationof systems (i.e., an audio augmented weapon locating system) can beprocessed to more accurately determine the location of the fired weapon,particularly at low quadrant elevations (QEs).

The radar system 102 can be capable of detecting and tracking one ormore projectiles fired from a weapon. In some embodiments, the radarsystem 102 can be a phased array radar system, also known as anelectronically scanned array (“ESA”), which is a type of radar systemthat uses multiple antennas to transmit and/or receive radiofrequency(RF) signals at shifted relative phases. The phase shifting thus allowsthe transmitted and/or received RF energy to be transmitted and/orreceived as transmit and/or received beams that can be electronically“steered” without the need to physically move components of the radarsystem. Examples of such a phased array radar system used in aconventional non-augmented weapon locating system include the AN/TPQ-36and the AN/TPQ-37 Firefinder Weapon Locating Systems manufactured byRaytheon Company of Waltham, Mass.

In some embodiments, the phased array can be comprised of transmitand/or receive elements disposed within a common assembly. In some otherembodiments, the phased array can be comprised of transmit and/orreceive antennas that a spatially separated and not disposed within acommon assembly. Although phased array radar systems can be an effectivechoice for the radar system 102, other types of radar systems may alsobe suitable. The radar system 102 can be stationary or mounted on amobile platform.

In one embodiment, the radar system 102 includes an antenna system 110,one or more transmitters 112, and one or more receivers 114. In someembodiments, the transmit and receive functions can be provided by acombined transmit/receive module. While not shown for clarity, it willbe understood that the radar system 102 can also include variouscomponents such as controllers, duplexers, oscillators, mixers,amplifiers, synchronizers, modulators, antenna positioning systems,power supply systems, data storage devices, and signal pre-processingequipment.

The audio sensor system 104 can comprise any type of sensor systemcapable of detecting and processing sound information. For example, theaudio sensor system 104 can include one or more transducers 116sensitive to sound information for a given frequency range. It isunderstood that a series of transducers optimized for particularfrequency ranges can be used to cover a desired aggregate frequencyrange. A signal processing module 118 can process the sensorinformation, as described more fully below.

A variety of sound sensor types can be used. The sensors may be locatedon the radar or the sensors may be located to form a network of sensorsfor determining the azimuth and elevation of a projectile solution. Itis understood that the temperature and humidity of the environment canbe used to calculate the speed of sound. In one embodiment, the systemcan process audio profiles of different types of devices to determinethe type of device fired. Such profiles can be stored in a database, forexample.

As used herein, the term “state vector” is used to describe a collectionof parameters (i.e., one or more parameters) that correspond to set ofcharacteristics of a moving projectile. The one or more state parameterswithin a state vector can include, but are not limited to, a position(in a coordinate system), a time, a speed, a heading (or threedimensional velocity vector), and acceleration in one or moredimensions, of the moving projectile.

As used herein, the term “backtracking” is used to describe a process bywhich one or more state vectors, each describing one or more parametersassociated with a projectile at a respective one or more positions alonga trajectory, can be extrapolated backward in time and space to identifya state vector associated with the projectile at an earlier point alongthe trajectory. The state vector at the earlier time and space caninclude both an earlier time and a location of the projectile at theearlier time. As used herein, the term “terrain” is used to describetopographical characteristics of the earth's surface. The terrain can berepresented by numerical values.

In general, electromagnetic radiation is classified by wavelength intoradio, microwave, infrared, visible, ultraviolet, X-rays, and gammarays, in order of decreasing wavelength. As used herein, the term“light” is used to describe at least electromagnetic radiation having awavelength in the infrared, visible, or ultraviolet portions of theelectromagnetic spectrum. Similarly, the term “optical” is used hereinto describe a system or component (e.g., sensor that interacts with orthat processes the infrared, visible, or ultraviolet portions of theelectromagnetic spectrum. As used herein, “sound” is used to describe asvibrations that travel through the air or another medium.

FIG. 2 shows an exemplary system 200 having at least one radar system202 a-N and at least one audio sensor system 204 a-M. The radar systems202 and audio sensor systems 204 are coupled to a signal processor 206that can fuse the radar and audio sensor information to locate a weaponsystem 20 firing a projectile 22. The signal processor 206 can generatean output signal indicative of one or more of a time of a detectedfiring event, an azimuth bearing of the detected firing event, or anelevation angle of the detected firing event.

In one embodiment, the audio sensor systems 204 are located proximate orattached to a respective radar system. In an alternative embodiment, theaudio sensors are located at locations separated from the radar systems.In one embodiment, audio sensors systems 204 can be launched and/ordropped in the area suspected to contain a weapon system. The audiosensors 204 can include a GPS receiver to determine its location andreport this and other information to the signal processor 206 or otherentity. In other embodiments, audio sensors are remote from othercomponents of the audio sensor systems.

The signal processing system 206 can include one or more computerprocessors, a data storage system, an output interface, a networkinterface, and software for processing the signals received from theaudio sensor system(s) 204 and the radar system(s) 202. Other hardware,firmware, and software can also be incorporated into the signalprocessing system 206. The signal processing system 206 can also includea communication system for transmitting, via either wired or wirelessconnection, data to a response system. The communicated data may includea set of fired weapon location coordinates.

The response system 208 can include, for example, a counter fire weaponsystem capable of returning fire to the location of the fired weapon, afriendly fire detection system capable of determining the location ofallied forces, or a threat assessment system for use by peace-keeping orlaw enforcement agencies to determine a location for follow-upinvestigation or patrol.

As described more fully below, the weapon locating system 200 can beused to determine a location from which a weapon is fired. The weaponmay fire any type of projectiles including shells, shot, missiles, orrockets.

Referring now to FIG. 3, when a weapon fires a projectile from alocation 330, the projectile follows a trajectory 332. While thetrajectory is shown to be a straight line, it will be understood thatthe trajectory need not be a straight line.

A quadrant elevation (QE) is an angle between an axis 336 upon ahorizontal plane and an axis of a bore of the weapon fired from thelocation 330. A firing azimuth, α, is an angle formed between an axis331 between the firing location 330 and the radar system 102 (of theweapon locating system 100) and the axis 336.

Acquisition, i.e. detection and tracking, of the fired projectile by theradar system 102 can occur at a location 338 along the trajectory 332.Associated with the location 338, the radar system 102 can generate astate vector that describes one or more characteristics of theprojectile and of the trajectory of the projectile. The radar system 102can make other detections at other points along the trajectory and canform other associated state vectors.

Conventionally, without use of the audio sensor system 104, the radarsystem 102 and signal processing system 106 can backtrack the resultingone or more state vectors to identify a state vector that intersects theterrain. Conventionally, the intersection can identify the location 330of the weapon that fired the projectile. However, particularly at lowQE, the identification of the location 330 is not precise.

An error associated with the radar system 102 (without use of the audiosensor system 104 (and neglecting radar ranging errors that aregenerally small compared to angular errors) can be characterized as an“error ellipse” 340 lying along the line-of-fire having a down rangeerror component σ_(DOWN) 342 and a cross range error component σ_(CROSS)344. The error components 342, 344 of the error ellipse 340 can becalculated as follows:

$\sigma_{DOWN} = \sqrt{\frac{{{VR} \cdot \sigma_{ɛ}^{2}} + \sigma_{ɛ - {bias}}^{2}}{\tan^{2}({QE})} + {( {{{VRR} \cdot \sigma_{\eta}^{2}} + \sigma_{\eta - {bias}}^{2}} ){\sin^{2}(\alpha)}}}$$\sigma_{CROSS} = \sqrt{( {{{VR} \cdot \sigma_{\eta}^{2}} + \sigma_{\eta - {bias}}^{2}} ){\cos^{2}(\alpha)}}$${VRR} = \frac{1 + {12( \frac{N - 1}{N + 1} )( {\frac{T_{BACK}}{T_{TRACK}} + 0.5} )^{2}}}{N}$

-   -   where:    -   σ_(ε)=random component (1 sigma) of the estimated target height        in meters;    -   σ_(ε-bias)=bias component of the estimated target height in        meters;    -   σ_(η)=random component (1 sigma) of the estimated azimuth error        in meters;    -   σ_(η-bias)=bias component (1 sigma) of the estimated azimuth        error in meters;    -   α=firing azimuth angle in radians;    -   VR=VRR (in this example a single filter type is used);    -   VRR=Variance reduction from filter smoothing (non-dimensional);    -   T_(BACK)=the total time the projectile is tracked by the radar        in seconds;    -   T_(TRACK)=that portion of the projectile flight time where        extrapolation is required in seconds;    -   N=number of measurements processed by the radar.

As can be seen from the equations above, as QE becomes a small angle andapproaches zero (i.e. direct fire), error in locating the fired weaponusing the radar system 102, particularly the down range error componentσ_(DOWN) 342, becomes greatly exaggerated and approaches infinity.Minimizing the error components improves the accuracy with which theweapon firing location 330 can be determined.

FIG. 4 shows an exemplary sequence of steps 450 for determining thelocation of a weapon firing system by combining radar and audio sensorinformation in accordance with exemplary embodiments of the invention.

As further discussed above, conventional backtracking of a state vectorassociated with a sequence of radar measurements backtracks the statevector until the backtracked state vector intersects a position in spaceidentified by the backtracked state vector intersecting the terrain. Theintersection in space can provide, within the intersecting state vector,a prediction in space of a location of a weapon, and also a predictionin time of when the weapon was fired. In contrast, techniques describedbelow can backtrack the state vector until the backtracked state vectorintersects a time identified by the backtracked state vectorintersecting a time identified by the above-described audio sensorsystem 104. This intersection in time can also provide, within theintersecting state vector, a prediction in space of a location of theweapon and also a prediction in time (known by the audio sensordetection in time) of when the weapon was fired.

Thus, both the conventional non-augmented weapon locating system and theaudio-augmented weapon locating system can provide both a prediction ofa location of a weapon and either a prediction of or knowledge of, atime of firing of the weapon.

In step 452, a weapon firing event occurs, resulting in sound thatpropagates both directly and indirectly from the weapon to the audiosensor system, for example, to the audio sensor system 104 of FIG. 1.The sound tends to have a time duration in accordance with the type ofweapon fired. For example, if the sound occurs due to a gun firingevent, the sound can have a duration in the order of milliseconds. Thesound can result from an explosive event, e.g., a gunshot, or acontrolled firing event, e.g., a rocket, etc.

In general, the beginning of the sound is indicative of a weapon firingevent, however, for some types of weapon firing events, it may bedesirable to mark the time of the weapon firing event as being a bitlater in time, for example, if the sound is generated by a prolongedrocket blast and the projectile is a rocket that accelerates relativelyslowly.

The audio sensor system 104 may use the time duration of the audio eventto classify the event as to the sound's source. The time history may beused to discriminate out non-firings or to classify the firing event asto type (e.g., rocket, mortar, artillery, etc.). When classificationdata is available to the radar system 102, the radar system can use theclassification data to improve ballistic estimator performance throughbetter modeling of the projectile, to adjust the projectile's firingtime to reflect the time the projectile actually began to leave thelunch platform (for example, rockets may require time to build thrust)and to eliminate possible false radar detections.

At step 454, an audio detection of a weapon firing event occurs wherethe audio sensor system. 104 detects the sound associated with theweapon firing event 452. At step 456, the time of the detection event454 can be stored, for example in a memory device associated with theaudio sensor system 104 or with the signal processing system 106. Insome embodiments, the audio sensor system 104 is directional, in whichcase, a bearing (i.e., direction) associated with the detection eventcan also be stored. The audio sensor system 104 may have directionalmeasurement capability in both bearing and elevation. When the audiosensor system 104 can measure direction, a means of aligning the audiosystem with the radar is provided. For example, a microphone array canperform beamforming to determine event direction.

At step 458, a common time base for the radar system 102 and for theaudio sensor system 104 is established, for example using a globalpositioning system (GPS), inter-range instrumentation group (IRIG) timecodes, or still another type of common clock. The common clock can beabsolute or relative. This synchronization of the times for the systems102, 104 will generally occur before the weapon firing event 452 and canbe scheduled to occur with regularity so that the systems staysynchronized.

At step 460, a radar acquisition event, i.e., a radar detection of aprojectile, occurs in which state information, such as altitude, speed,direction, acceleration, and time, associated with the projectile at thelocation 338 (FIG. 3) along the trajectory 332 (FIG. 3) is collected.The radar acquisition event, i.e., the radar detection, can occur afterthe weapon firing event detected by the audio sensor system 1-4 at block454.

At step 462, the radar system 102, either alone or together with thesignal processing system 106, forms a state vector using the stateinformation associated with the projectile at location 338. At step 464,a correlation between the audio detection event 454 and the radaracquisition event 460 is made, if possible, using the stored event timeand, in some embodiment, bearing data.

The correlation can be made in a number or ways. For example, in someembodiments, the correlation is made by comparing the time of the audiodetection event with a time of the radar detection. A time differencethreshold can be established based upon the environment (i.e., theapplication) in which the system is used, and any time difference lessthan the time difference threshold can be indicative of a correlation.For example, if the system is used to detect locations of missile firingevents, the time difference threshold can be relatively large, forexample, 5 seconds. For another example, if the system is used to detectlocations of close range gun firing events, the time differencethreshold can be relatively small, for example, 0.1 seconds. Other timedifference thresholds are possible.

As described above and further below, backtracking the state vector insteps below provides both a weapon firing location estimate and a firingtime estimate.

In other embodiments, correlation can be established by comparing thetime of the weapon firing event detected by the audio sensor system 104(FIG. 1) with a time of the radar detection of the projectile when thestate vector of the projectile is conventionally backtracked tointersect the terrain. A time difference threshold can be establishedbased upon the environment (i.e., the application) in which the systemis used, and any time difference less than the time difference thresholdcan be indicative of a correlation. For example, if the system is usedto detect locations of missile firing events, the time differencethreshold can be relatively large, for example, 5 seconds. For anotherexample, if the system is used to detect locations of close range gunfiring events, the time difference threshold can be relatively small,for example, 0.1 seconds. Other time difference thresholds are possible.

In other embodiments, correlation can be established by comparingresults of the conventional backtracking of the radar state vector tointersect the terrain with the backtracking described herein and belowthat backtracks the radar state vector to a point in time (and resultingspace) established by the audio sensor system 104. As described above,both methods generate a prediction of a position from which the weaponwas fired. A position difference threshold can be established based uponthe environment (i.e., the application) in which the system is used, andany position difference less than the position difference threshold canbe indicative of a correlation. Other position difference thresholds arepossible.

With regard to the above correlation that backtracks the state vector inconventional and also in audio enhanced ways, from discussion above, itwill be understood that, for low QEs, the conventional method toestimate weapon position may have very large errors, thus the abovecorrelation using a position difference threshold may only apply to QEsabove a threshold QE.

In still other embodiments for which the audio sensor system 104provides directional information, e.g., azimuth bearing and/or elevationangle of a detected firing event, correlation can be established bycomparing the azimuth bearing and or the elevation angle reported by theaudio sensor system 104 with the azimuth bearing and/or the elevationangle reported by the radar system 102. An azimuth angle differencethreshold and/or an elevation angle difference threshold can beestablished based upon the environment (i.e., the application) in whichthe system is used, and any azimuth angle difference and/or elevationangle difference less than azimuth angle difference threshold and/orelevation angle difference threshold can be indicative of a correlation.For example, if the system is used to detect locations of missile firingevents, the azimuth angle difference threshold and/or the elevationangle difference threshold can be relatively large, for example, both10.0 degrees. For another example, if the system is used to detectlocations of close range gun firing events, the azimuth angle differencethreshold and/or the elevation angle difference threshold can berelatively small, for example, both 1.0 degrees. Other angle differencethresholds are possible.

It should be understood that any one or more of the above-describedtechniques can be used to identify a correlation between radar detectedevents and filing events detected by the audio sensor system 104. Somecorrelations can be deemed to be primary and others can be deemed to besecondary, in any combination. Other correlation techniques are alsopossible, including techniques that make use of the directionalcapability of some audio sensor systems.

At step 466, a determination is made as to whether the weapon firingevent detected by the audio sensor system at block 454 and the radaracquisition event detected by the radar system 102 at block 460correlate. If a correlation cannot be made, at step 468 a potential (andpossibly less accurate) weapon firing location can be determined byconventionally backtracking the state vector until it intersects theterrain topography. Extrapolation techniques can be used to perform thebacktracking.

If a correlation can be made, at step 470 a more accurate weapon firinglocation can be determined by the audio augmented weapon locating system100 (FIG. 1) by backtracking the state vector, not to an intersectionwith the terrain, but instead to an intersection in time with the weaponfiring event time identified by the audio sensor system 104.Extrapolation and/or interpolation techniques can be used to perform thebacktracking. Geographic coordinates associated with the backtrackedstate vector at the weapon firing event time identified by the audiosensor system 104 are calculated to establish a likely location of theweapon that fired the projectile. This calculated location of the weaponis more accurate than that described above using the radar system 102alone.

At step 472, the coordinates associated with the likely location of thefired weapon are communicated to the response system 108 (FIG. 1). Theresponse system 108 can direct a counter fire weapon capable ofreturning fire to the location of the fired weapon. Alternatively, theresponse system 108 can associate the location of the fired weapon withfriendly fire from allied forces for purposes of mapping the location ofallied forces. In still another alternative, the response system 108 canmap the location of the fired weapon for use by peace-keeping or lawenforcement agencies to determine a geographic area for follow-upinvestigation or patrol.

Referring now to FIG. 5, a graph 580 compares down range error atvarious quadrant elevations liar one example of a non-augmentedconventional weapon locating system having only a radar system and oneexample of an audio augmented weapon locating system having both a radarsystem and an audio sensor system. Alternative embodiments ofaudio-augmented and non-augmented conventional weapon locating systemsmay result in different error responses. In the illustrative embodimentof FIG. 5, the plotted data set 582 shows a relationship between the QEof a firing weapon and the down range error component (σ_(DOWN))associated with the use of a non-augmented conventional weapon locatingsystem having the radar system 102 but not the audio sensor system 104.The graph 580 shows the general relationship between QE and down rangeerror associated with the non-augmented conventional weapon locatingsystem. As the QE of the firing weapon approaches 0, the error increasesexponentially, rendering the non-augmented conventional weapon locatingsystem relatively ineffectual in determining the location, of the firingweapon.

A plotted data set 582 shows a relationship between the QE of the firedweapon and the down range error component associated with the use of anaudio augmented weapon locating system, e.g., 100 of FIG. 1, having botha radar system and an audio sensor system. The down range comparisongraph 580 shows that backtracking the state vector of a projectile, asformed by a non-augmented conventional weapon locating system, to a timeassociated with a weapon firing event, as detected by an audio sensorsystem in an audio-augmented weapon locating system, results in improvedweapon locating for low QE values of the firing weapon. It is understoodthat the results presented in FIG. 5 are just one example ofaudio-augmented and non-augmented conventional weapon locating systemdown range error values. For alternative embodiments, using differentradar and audio sensor systems, the results may vary.

FIG. 6 shows an exemplary weapon locating system 600 including a radarsystem 602 and an optical sensor system 604, both of which communicatesignals to a signal processing system 606. The optical sensor system 604and/or an audio sensor system 616 can provide information to the signalprocessing system 606. Optionally, the signal processing system 606 cantransmit information derived from the received signals to a responsesystem 608. The optical sensor system 604 is also referred to as anelectro-optical (EO) system herein. The optical sensor system 604 can beany type of optical sensor system capable of detecting and processinglight. For example, the optical sensor system 604 can comprise anelectro optical (EO) sensor system.

FIG. 7 shows an exemplary computer 700 that can perform at least part ofthe processing described herein. The computer 700 includes a processor702, a volatile memory 704, a non volatile memory 706 (e.g., hard disk),an output device 707 and a graphical user interface (GUI) 708 (e.g., amouse, a keyboard, a display, for example). The non-volatile memory 706stores computer instructions 712, an operating system 716 and data 718.In one example, the computer instructions 712 are executed by theprocessor 702 out of volatile memory 704. In one embodiment, an article720 comprises non-transitory computer-readable instructions.

Processing may be implemented in hardware, software, or a combination ofthe two. Processing may be implemented in computer programs executed onprogrammable computers/machines that each includes a processor, astorage medium or other article of manufacture that is readable by theprocessor (including volatile and non-volatile memory and/or storageelements), at least one input device, and one or more output devices.Program code may be applied to data entered using an input device toperform processing and to generate output information.

The system can perform processing, at least in part, via a computerprogram product, (e.g., in a machine-readable storage device), forexecution by, or to control the operation of data processing apparatus(e.g., a programmable processor, a computer, or multiple computers).Each such program may be implemented in a high level procedural orobject-oriented programming language to communicate with a computersystem. However, the programs may be implemented in assembly or machinelanguage. The language may be a compiled or an interpreted language andit may be deployed in any form, including as a stand-alone program or asa module, component, subroutine, or other unit suitable for use in acomputing environment. A computer program may be deployed to be executedon one computer or on multiple computers at one site or distributedacross multiple sites and interconnected by a communication network. Acomputer program may be stored on a storage medium or device (e.g.,CD-ROM, hard disk, or magnetic diskette) that is readable by a generalor special purpose programmable computer for configuring and operatingthe computer when the storage medium or device is read by the computer.Processing may also be implemented as a machine-readable storage medium,configured with a computer program, where upon execution, instructionsin the computer program cause the computer to operate.

Processing may be performed by one or more programmable processorsexecuting one or more computer programs to perform the functions of thesystem. All or part of the system may be implemented as, special purposelogic circuitry (e.g., an FPGA (field programmable gate array) and/or anASIC (application-specific integrated circuit)).

All references cited herein are hereby incorporated herein by referencein their entirety. Having described preferred embodiments, which serveto illustrate various concepts, structures and techniques, which are thesubject of this patent, it will now become apparent to those of ordinaryskill in the art that other embodiments incorporating these concepts,structures and techniques may be used. Accordingly, it is submitted thatthat scope of the patent should not be limited to the describedembodiments but rather should be limited only by the spirit and scope ofthe following claims.

What is claimed is:
 1. A method of locating a weapon, comprising:detecting a weapon firing event with an audio sensor system, thedetected weapon firing event indicative of a detected firing of theweapon and indicative of a detected time of the weapon firing event;detecting a projectile fired from the weapon with a radar system;employing a processor configured for: correlating the weapon firingevent detected by the audio sensor system with the detection of theprojectile by the radar system to determine if the weapon firing eventdetected by the audio sensor system corresponds to the same projectileas that detected by the radar system, wherein the correlating comprises:selecting a time difference threshold; and relating the time differencethreshold to a difference between the detected time of the weapon firingevent detected by the audio sensor system and a time of the detection ofthe projectile by the radar system; calculating a state vectorassociated with the projectile detection; identifying a location of theweapon by backtracking the state vector to the detected time of theweapon firing event time; and communicating the location of the weapon.2. The method of claim 1, further comprising generating a common timebase for the weapon firing event and for the projectile detection. 3.The method of claim 1, wherein the audio sensor system comprises anaudio sensor.
 4. The method of claim 1, wherein the audio sensor systemis directional and provides at least one of an azimuth angle of thedetected weapon firing event or an elevation angle of the detectedweapon firing event.
 5. The method of claim 1, wherein the step ofdetecting the weapon firing event with the audio sensor system comprisesdetecting the weapon firing event by direct path detection of audiogenerated by the weapon firing event.
 6. A method of locating a weapon,comprising: detecting a weapon firing event with an audio sensor system,the detected weapon firing event indicative of a detected firing of theweapon and indicative of a detected time of the weapon firing event;detecting a projectile fired from the weapon with a radar system;employing a processor configured for: correlating the weapon firingevent detected by the audio sensor system with the detection of theprojectile by the radar system to determine if the weapon firing eventdetected by the audio sensor system corresponds to the same projectileas that detected by the radar system, wherein the correlating comprises:selecting a time difference threshold; and relating the time differencethreshold to a difference between a time predicted by the state vectorwhen backtracked to a terrain and the detected time of the weapon firingevent detected by the audio sensor system; calculating a state vectorassociated with the projectile detection; identifying a location of theweapon by backtracking the state vector to the detected time of theweapon firing event time; and communicating the location of the weapon.7. A method of locating a weapon, comprising: detecting a weapon firingevent with an audio sensor system, the detected weapon firing eventindicative of a detected firing of the weapon and indicative of adetected time of the weapon firing event; detecting a projectile firedfrom the weapon with a radar system; employing a processor configuredfor: correlating the weapon firing event detected by the audio sensorsystem with the detection of the projectile by the radar system todetermine if the weapon firing event detected by the audio sensor systemcorresponds to the same projectile as that detected by the radar system,wherein the correlating comprises: selecting a position differencethreshold; and relating the position difference threshold to adifference between a location predicted by the state vector whenbacktracked to a terrain and a location predicted by the state vectorwhen backtracked to the detected time of the weapon firing eventdetected by the audio sensor system; calculating a state vectorassociated with the projectile detection; identifying a location of theweapon by backtracking the state vector to the detected time of theweapon firing event time; and communicating the location of the weapon.8. A method of locating a weapon, comprising: detecting a weapon firingevent with an audio sensor system, the detected weapon firing eventindicative of a detected firing of the weapon and indicative of adetected time of the weapon firing event; detecting a projectile firedfrom the weapon with a radar system; employing a processor configuredfor: correlating the weapon firing event detected by the audio sensorsystem with the detection of the projectile by the radar system todetermine if the weapon firing event detected by the audio sensor systemcorresponds to the same projectile as that detected by the radar system,wherein the correlating comprises: selecting an angle differencethreshold; and relating the angle difference threshold to a differencebetween an angle to the projectile identified by the radar system and anangle to the weapon identified by the audio sensor system; calculating astate vector associated with the projectile detection; identifying alocation of the weapon by backtracking the state vector to the detectedtime of the weapon firing event time; and communicating the location ofthe weapon.
 9. A weapon locating system, comprising: an audio sensorsystem configured to detect a weapon firing event, the detected weaponfiring event indicative of a detected firing of the weapon andindicative of a detected time of the weapon firing event; a radar systemconfigured to detect a projectile fired from the weapon; a processorconfigured to: correlate the weapon firing event detected by the audiosensor system with the detection of the projectile by the radar systemto determine if the weapon firing event detected by the audio sensorsystem corresponds to the same projectile as that detected by the radarsystem, wherein the correlating comprises: selecting a time differencethreshold; and relating the time difference threshold to a differencebetween the detected time of the weapon firing event detected by theaudio sensor system and a time of the detection of the projectile by theradar system; and calculate a state vector associated with theprojectile detection and to backtrack the state vector to the detectedtime of the weapon firing event to identify the location of the weapon;and a communication system configured to communicate the location of theweapon.
 10. An article, comprising: at least one computer-readablemedium containing non-transitory stored instructions that enable amachine to perform: detecting a weapon firing event with an audio sensorsystem, the detected weapon firing event indicative of a detected firingof the weapon and indicative of a detected time of the weapon firingevent; detecting a projectile fired from the weapon with a radar system;correlating the weapon firing event detected by the audio sensor systemwith the detection of the projectile by the radar system to determine ifthe weapon firing event detected by the audio sensor system correspondsto the same projectile as that detected by the radar system, wherein thecorrelating comprises: selecting a time difference threshold; andrelating the time difference threshold to a difference between thedetected time of the weapon firing event detected by the audio sensorsystem and a time of the detection of the projectile by the radarsystem; calculating a state vector associated with the projectiledetection; identifying a location of the weapon by backtracking thestate vector to the detected time of the weapon firing event time; andcommunicating the location of the weapon.
 11. The method of claim 1,further including receiving data from an optical sensor system toidentify the location of the weapon.
 12. The system of claim 9, furtherincluding an optical sensor system coupled to the radar system.